One of the approaches to flood modelling is numerical simulation of the diffusive wave approximation of the shallow water equations. Improving these models in various aspects is still an open area of research. In this study, a new diffusive wave model with explicit time integration was developed which includes some novel features: (1) time steps are determined using a novel stability criterion which resulted in more dynamic time steps (i.e., broader range) compared to the conventional Courant–Friedrichs–Lewy stability condition; (2) stability constraints are reduced, considering the flow processes within surface ponds; (3) besides Manning's formula, which is the common equation for computing velocities in diffusive wave models, the free fall velocity and a new equation for wave-front velocity are employed; and (4) the influence of upstream surface ponds on downstream flow is considered. This paper introduces the enhanced diffusive wave model, the so-called Overland Flow Simulator Cellular Automata (OFS-CA), and its results for five test cases. Available analytical solutions and an experimental study were used for verification. Two other shallow water models were used for comparison and benchmarking. Overall, good agreements were observed and OFS-CA was computationally less expensive compared to the other two shallow water models.

Transient flows differ from steady flows in the sense that their dynamic variables, e.g. velocity, change with time. This imposes several constraints both on the measurement techniques to use as well on the data processing. The dam-break flow, as an example of severe transient flow, is used in this paper as test case for the application of different statistical methods identified in the literature: the common statistical tools (e.g. time average, standard deviation), the application of a Fourier-series-based method and the ensemble statistics approach. Data were collected using a fast acquisition camera and particle image velocimetry was used to obtain quantitative information about the velocity field of a set of seven dam-break flows. From the analysis made in this paper it was possible to identify in which conditions each statistical method can be applied to the dam-break flow.

The present work addresses the influence of internal drainage systems on failure by overtopping of earth dams. It is based on data collected in six homogeneous dam breach laboratory experiments. Different drainage systems were tested: (a) toe drain only and (b) complete internal drainage system—chimney filter, horizontal blanket and toe drain. The tests were performed with the same embankment body material, reservoir dimensions and inflow conditions but different relative compactions. We analyze the breach hydrograph and the stages of dam breaching. The failure of dams with complete and fully functional drainage systems exhibits marked differences, the most conspicuous of all being the longer duration of the initial erosion stage. This is accompanied by a lower increase rate of its breach discharge. We argue that this is the combined result of the upstream migration of the locus of hydraulic control and of a higher resistance to erosion of the downstream shell, kept unsaturated by the drainage system. Hydraulic control moves upstream, to a less morphologically active cross‐section, as a result of channel deepening once the chimney drain is uncovered and eroded. Once the erosion merges with the cavity where the chimney filter was, marking the end of the initial erosion stage, the rate of erosion increases and becomes comparable to that of dams with toe drain only. Our argument about the longer duration of the initial stage is not applicable to latter stages—the total time before full collapse is not necessarily increased.

Channel bed morphology depends on bedload fluxes which are difficult to determine even in controlled laboratory conditions. Particle counting can provide time resolved bedload fluxes. Determination of particle rates by means of digital image processing is computationally expensive and the requirement for optical access is not always met. Weighing methods are limited by short dynamic ranges. To overcome these difficulties this paper presents a prototype of a particle counter device that works by detecting impacts on a sensitive surface. The accuracy of the device is validated, by means of laboratory experiments, contrasting its results against those obtained by means of digital image analysis. This device proved to be capable of measuring bedload fluxes, determining long time series of bedload transport rates, in particles per unit time, with high accuracy and with a much lower computation cost relatively to digital image processing. The device is also able to gather meaningful data in real-time, like particle arrival time-series and real-time lateral bedload distribution. The parameters involved in the detection criterion must be previously set through a heuristic procedure. However, the method itself is direct—it requires no calibration between the acquired signal and bedload transport rates. Particle counts can be transformed in bedload discharges by a simple binning process or by taking finite differences of the cumulative mass function. First and second order moments of bedload discharge are in agreement with the values obtained by direct counting. The low requirement for data storage, allowing for very large data series, the real time analysis capabilities, the low cost of such system when compared with a digital image acquisition system constitute the main advantages of the device for the study of integral scales of bedload and bedload intermittency.